6A44.52 - Total Internal Reflection - Laser and Block

Code Number:
6A44.52
Demo Title:
Total Internal Reflection - Laser and Block
Condition:
Excellent
Principle:
Critical Angle and Total Internal Reflection
Area of Study:
Optics
Equipment:
Adjustable Laser, Black Board Optics Refraction Block, White Paper.
Procedure:

Place the square block from the Black Board Optics set on a white piece of paper with the frosted side towards the audience.  Point a laser straight down into the block and turn it on.  The laser beam reflects off the paper and into the higher density medium of the block creating the cone of light you observe.  This cone describes the critical angle in exactly the same way as if you were at the bottom of a pool of water and looking up and out of the pool.  You would be able to see out of the water inside the cone, but would see nothing but a mirror effect if trying to look outside that critical angle.

References:
  • James Lincoln, "The Circle of Light: A New Lab on Total Internal Reflection", TPT, Vol. 60, #7, Oct. 2022, p. 618.
  • Barret R. Viss and Arnold E. Sikkema, "A Demonstration of the Critical Angle Without Using Total Internal Reflection", TPT, Vol. 43, #7, Oct. 2005, p. 471.
  • S. Reich, "Measurement of Refractive Index in Transparent Plates with a Piece of Paper and a Laser Source", AJP, Vol. 51, #5, May 1983, p. 469.
  • D. C. Look, Jr., "Novel Demonstration of Total Internal Reflection", AJP, Vol. 49, #8, Aug. 1981, p. 794.

Disclaimer: These demonstrations are provided only for illustrative use by persons affiliated with The University of Iowa and only under the direction of a trained instructor or physicist.  The University of Iowa is not responsible for demonstrations performed by those using their own equipment or who choose to use this reference material for their own purpose.  The demonstrations included here are within the public domain and can be found in materials contained in libraries, bookstores, and through electronic sources.  Performing all or any portion of any of these demonstrations, with or without revisions not depicted here entails inherent risks.  These risks include, without limitation, bodily injury (and possibly death), including risks to health that may be temporary or permanent and that may exacerbate a pre-existing medical condition; and property loss or damage.  Anyone performing any part of these demonstrations, even with revisions, knowingly and voluntarily assumes all risks associated with them.